Because they are easily seen, it may seem that the male sex organs are rather simple, but this is not the case. The penis, which is composed of many parts, contains an amazing and complex hydraulic system.
Penises are individual, coming in a wide range of shapes, sizes, and colorations. Some grow a great deal when they become erect, while others become hard without much change in size. When erect, some point straight out, others hang down, and still others become almost vertical.
The penis is composed of three chambers; the two cavernous bodies (or corpora cavernosa) which lie side by side on top of the penis, and the spongy body (or corpus spongiosum) which is centered below the other two. The spongy body surrounds the urethra, and extends out the end of the shaft to form the glans. All three chambers contain small hollow areas that can fill with blood to produce an erection. Surrounding all three bodies is a semi-elastic membrane called the tunica albuginea. The arteries that feed blood to the penis are surrounded by smooth muscle fibers that normally limit blood flow to the penis. When a man is aroused by thought, sight, or physical stimulation, the muscle fiber relaxes and blood flow into the penis increases. The spongy tissue of the penis fills with blood, causing the penis to swell. The size of the erect penis is governed by the semi-elastic membrane, just as a bicycle tire limits the expansion of the inner tube inside it. As with a bike tire, once the limit of the membrane is reached, further pressure results in firmness rather than expansion. The veins that drain the penis, which lie close to the surface, are compressed by the erection, thus slowing flow of blood from the penis.
The part of the penis that is visible is only about half of the whole organ. The root of the penis is the portion of the penis that is inside the body. The root is attached to bone at its base, and this serves to anchor the penis and allows it to stand away from the body during erection.
Some men worry about the size of their penis. Since only the first 2 to 3 inches of the vagina has nerve endings, length has little to do with pleasing a wife during intercourse. Statistically, 90% of erect penises are 6 inches or shorter. Non-erect size is not an accurate determiner of erect size.
The shaft of the penis contains neither bone nor any significant amount of muscle. The shaft is wider than it is high, and one side usually bulges out more than the other. The erect penis is very tough, it can be squeezed quite firmly without causing pain or damage. The most common complaint men have about the way their wife handles their penis is “she’s too gentle.”
Only about half the penis shows externally, the rest is inside the body. The internal part of the penis also becomes erect. The cavernous bodies attach to the pelvic bone, while the spongy body continues back almost to the anus; during erection this part of the penis can be felt behind the scrotum.
Also called the head of the penis, the glans contains a large number of nerve endings, making it the most sensitive part of the penis. The frenulum is the most sensitive area, the corona the second most sensitive area. In most men, the glans is hypersensitive right after orgasm.
At birth the glans is covered by a retractable skin called the foreskin, which is frequently removed by circumcision. Aside from religious reasons, circumcision has been normally performed for supposed hygienic reasons. Recent data suggest that daily washing is as effective as circumcision in maintaining cleanliness and that the foreskin serves several purposes. Circumcision is a routine operation in America, but virtually nonexistent (other than for religious reasons) in Europe.
The scrotum is composed of skin and muscle, and is designed to pull the testicles closer to the body for warmth, and to hang away from the body for cooling. The scrotum also pulls the testicles towards the body during sexual excitement, and at climax they are held tightly against the body. One side of the scrotum, usually the left, hangs slightly lower to keep the testicles from knocking together when a man walks or runs.
Also called the testes. Both sperm and male sex hormones are produce by the testicles. Sperm production requires a temperature slightly below normal body temperature, and new research suggests that temperature also effects hormone production. The testicles are very sensitive to pressure; even a slight bump can be painful. While many men like to have their testicles stimulated, the wife should use great care.
Once produced in the testicles, sperm move into the epididymis to “ripen”. At this point the sperm are inactive, being moved by the body, not by swimming.
The vas deferens are thin tubes that transport sperm from the epididymis up into the body.
The vas deferens end near the seminal vesicles, which produce part of the fluid ejaculated with the sperm. See Physiology of the Male Sex Drive for more information.
This gland produces a part of the seminal fluid, begins the ejaculation process, and keeps semen and urine from mixing. The prostate produces small amounts of fluid continually, but accelerates greatly during sexual arousal. Since a man’s enjoyment of orgasm is effected by the quantity of his ejaculation, the extra fluid produced during prolonged arousal can lead to a stronger climax. Prostatitis or congested prostate is a painful condition caused by repeated arousal without ejaculation, or by a “feast-or-famine” sex life (such as that of a traveling salesman). Mild cases can be easily remedied by climaxing. More serious cases require prescription medication and massaging of the prostate by a physician. As a man ages his prostate swells, often interfering with normal urination. Prostate cancer is very common in older men, although it is treatable if found early by routine screening.
Small valves, the sphincters control the flow of urine and semen in the prostate. The upper sphincter prevents semen from moving into the bladder during ejaculation; it also makes it more and more difficult for a man to urinate as he becomes increasingly erect. The lower sphincter helps pressurize the semen just before ejaculation.
An area of the urethra in the prostate between the sphincters. The sperm and various fluids mix in this area as ejaculation begins, the closed sphincters and muscle contractions creating a pressurized system. Once this happens, climax cannot be stopped.
These two pea-sized glands produce a slippery alkaline fluid when the man is aroused. This fluid prepares the urethra for ejaculation. During prolonged arousal, the fluid may form drops at the tip of the penis. Sperm are not present in this fluid.
When a man is sexually stimulated by sight, thought, or touch, the brain sends signals that relax the smooth muscles around the arteries that supply blood to the spongy and cavernous bodies. The veins draining the bodies can’t keep up, resulting in swelling. As the swelling reaches the limit of the penile skin, the penis becomes firm. The pressure of the spongy and cavernous bodies against the skin partially closes the veins, helping to maintain the erection. Erection continues until the signals from the brain stop, but erections are not consistent; waking and waning are normal, even during intercourse. Erection can occur throughout life, happening before birth and into the 90’s in healthy men. Nocturnal erections occur during all male dreams (regardless of what the dream is about), unless the man has physical problems (this is the easiest way to determine if impotence is physical or emotional in nature). The so called “morning erection” is the result of being wakened during, or just after a dream; and it can be a very persistent erection. While a morning erection is not a sign of arousal, its presents and the pleasurable sensations it can create may result in arousal. Men have only very limited control over their erections. During puberty the young man is often embarrassed by erection in public settings, but he gradually becomes able to suppress erections when the stimulation is mild. Likewise, it is impossible to “will” an erection, although sexual thoughts can cause erection. During prolonged foreplay a man’s erection may go away; this is normal, and is not a sign of lessening interest. General health and physical exhaustion can affect erection; when very tired, a man may be able to have only a partial erection, but still be able to climax. Erection is lost in two stages; the initial stage is very quick, but usually leaves the penis firm enough to continue intercourse. The second stage is somewhat slower and is affected by a variety of things including age (which tends to speed it), and arousal level before climax, with higher (or longer) pre-climax arousal generally resulting in slower loss of erection.
A mixture of sperm cells (less than 1%) and fluids from the prostate (30%) and seminal vesicles (70%). A typical ejaculation is about a teaspoon of fluid, and can contain up to 600 million sperm.
This is the pleasurable feeling of sexual climax. In men orgasm lasts from four to eight seconds, and is more powerful if arousal is prolonged, or it’s been a long time since his last climax. Boys who begin masturbating before puberty experience “dry climaxes”; orgasm without ejaculation. Although rare, it is possible for a grown man to orgasm without ejaculating. Following orgasm the glans becomes hypersensitive. In a few men the sensitivity is so extreme that they are unable to continue intercourse following orgasm.
The expulsion of semen from the penis. Ejaculation normally happens along with orgasm, although it can be caused separately, such as the “electro-ejaculation” used to obtain semen from bulls. Ejaculation happens in two distinct parts. The first, the emission phase, causes sperm and fluid to mix in the ejaculatory duct, while the sphincters close and muscles contract. During this time the man feels what is called “ejaculatory inevitability” (or the point of no return). The second, or expulsion phase, occurs when the lower sphincter opens, forcing the semen out into the penis. Contractions in the base of the penis help propel semen out of the body. Most of the fluid is ejected in the first few contractions, but the penis may continue to contract sporadically for 15 to 20 seconds, particularly after prolonged arousal. During adolescence, the ejaculation is quite forceful, but it diminishes rapidly in the twenties. This is a normal change that does not affect fertility. The amount of semen in an ejaculation is normally about a teaspoon full, but this varies from man to man. If a man has two ejaculations in a short period of time the second will be very small.
Following ejaculation the penis returns to its non-erect state. There is a rapid partial loss of erection, followed by a much slower loss of the remaining erection. The second stage lose seems to be slower after prolonged sex. Resolution refers to the period of time after ejaculation during which a man can’t have another erection. While there is an obvious physical component to resolution (prepubescent boys, who don’t ejaculate, don’t have a resolution phase after orgasm), it seems to also be effected by the mind; some men can continue to a second climax without losing erection entirely. Over all, the length of the resolution phase is related to age, being minutes in teens and possibly days in elderly men; but this varies greatly, and seems to be effected by sexual frequency, with the least active men having the longest resolution phases as they age.
male genitals diagram © Lavreteva / Adobe Stock